In the prior art, automatic transmissions, especially ones for motor vehicles, comprise planetary gearsets which are shifted by means of frictional or shift elements such as clutches and brakes, and which are usually connected to a starting element that can be operated in slipping mode and can optionally be provided with a bridging clutch such as a hydrodynamic torque converter or a fluid clutch.
A transmission of this kind is described in EP 0 434 525 A1. It comprises essentially a drive input shaft and a drive output shaft arranged parallel to one another, a double planetary gearset arranged concentrically with the drive output shaft, and five shift elements in the form of three clutches and two brakes, whose selective engagement, in each case in pairs, determines the various gear ratios between the input shaft and the output shaft. The transmission also comprises an upstream gearset and two power paths, so that the selective engagement of the five shift elements, two at a time, produces six forward gears.
In this case, to transmit the torque from the upstream gearset to two elements of the double planetary gearset, two clutches are needed. In the force flow direction these are arranged essentially behind the upstream gearset, in the direction of the double planetary gearset. In the second power path a further clutch is provided, which releasably connects to another element of the double planetary gearset. The clutches are arranged so that the inner disk carrier forms the drive output.
Furthermore, from the document U.S. Pat. No. 6,139,463 a compact multi-step transmission of planetary structure, in particular for a motor vehicle is known, which comprises two planetary gearsets and an upstream gearset as well as three clutches and two brakes. In this known multi-step transmission, in a first power path the clutches C-1 and C-3 are provided for transmitting torque from the upstream gearset to the two planetary gearsets. In this case the outer disk carrier, the cylinder or piston and pressure compensation side of the clutch C-3 is connected to a first brake B-1. In addition, the inner disk carrier of the third clutch C-3 is connected to the cylinder, piston or pressure compensation side of the first clutch C-1, and the inner disk carrier of the first clutch C-1 is arranged on the drive output side and is connected to a sun gear of the third planetary gearset.
Furthermore, from DE 199 49 507 A1 by the present applicant a multi-step transmission is known, in which two non-shiftable upstream gearsets are provided on the drive input shaft, which produce two speeds on the output side which, besides the speed of the drive input shaft, can optionally be shifted through to a shiftable double planetary gearset that acts upon the drive output shaft, by selectively engaging the shift elements used in such manner that to shift from one gear into the respective next-higher or next-lower gear, of the two shift elements just actuated only one shift element has to be engaged or disengaged.
From DE 199 12 480 A1 an automatically shifted motor vehicle transmission is known, which has three single-carrier planetary gearsets as well as three brakes and two clutches for shifting between six forward gears and one reversing gear, and with a drive input and a drive output shaft. This automatically shifted motor vehicle transmission is designed in such manner that the drive input shaft is connected directly to the sun gear of the second planetary gearset, while the input shaft can be connected by means of the first clutch to the sun gear of the first planetary gearset and/or by the second clutch to the carrier of the first planetary gearset. In addition or alternatively, the sun gear of the first planetary gearset can be connected by the first brake to the housing of the transmission, and/or the carrier of the first planetary gearset can be connected by the second brake to the housing, and/or the sun gear of the third planetary gearset can be connected by the third brake to the housing.
Furthermore, from DE 102 13 820 A1 a multi-gear automatic transmission is known, which has an first input path T1 of a first transmission ratio; an input path T2 which has a larger transmission ratio than the input path T1; a planetary gearset with four elements, these four element being a first element, a second element, a third element and a fourth element in the sequence of elements in a speed diagram; a clutch C-2 which transmits rotation from the input path T2 to the first element S3; a clutch C-1 which transmits rotation from the input path T1 to the fourth element S2; a clutch C-4 which transmits rotation from the input path T1 to the first element; a clutch C-3 which transmits rotation from the input path T1 to the second element C3; a brake B-1 which engages the fourth element; a brake B-2 which engages the second element; and a drive output element, which is coupled to the third element R3.
In the context of DE 101 15 983 A1 by the present applicant a multi-step transmission is described, which has a drive input shaft connected to an upstream gearset, a drive output shaft connected to a downstream gearset, and a maximum of seven shift elements, by the selective shifting of which at least seven forward gears can be engaged without a range shift. The upstream gearset is formed by an upstream planetary gearset or a maximum of two non-shiftable upstream planetary gearsets coupled to the first upstream planetary gearset, while the downstream gearset is formed as a two-carrier, four-shaft transmission with two shiftable downstream planetary gearsets and four free shafts. The first free shaft of this two-carrier, four-shaft transmission is connected to the first shift element, the second free shaft to the second and third shift elements, the third free shaft to the fourth and fifth shift elements, and the fourth free shaft is connected to the drive output shaft. For a multi-step transmission with a total of six shift elements it is proposed according to the invention to connect the third free shaft or the first free shaft of the downstream gearset additionally to a sixth shift element (D′) and to connect the first free shaft additionally to a seventh shift element.
Furthermore, in the context of DE 101 15 987 by the present applicant a multi-step transmission with at least seven gears is described. Besides the drive input shaft and the drive output shaft this transmission consists of a non-shiftable upstream gearset and a shiftable downstream gearset in the form of a two-carrier, four-shaft transmission. The upstream gearset consists of a first planetary gearset which, besides the input speed of the drive input shaft, provides a second speed that can optionally be switched through to the downstream gearset. The downstream gearset consists of two shiftable planetary gearsets which, with the six shift elements, can engage at least seven gears, forming two power paths. In this case, during any shift operation, group shifts are advantageously always avoided. In addition, a 9-gear multi-step transmission is known from DE 29 36 969; this comprises eight shift elements and four gearsets.
DE 102 44 023 A1 by the present applicant describes a change-under-load transmission with positive-interlock and frictional shift elements, in which the positive-interlock shift elements have to be disengaged during upshifts in order to avoid any adverse effect on shift quality.
Automatically shifted vehicle transmissions of planetary structure in general have already often been described in the prior art and constantly undergo further development and improvement. Such transmissions are required to provide a sufficient number of forward gears and a reversing gear, and transmission ratios very well suited for motor vehicles, with a large overall spread and appropriate gear intervals. Furthermore, they should enable a high starting transmission ratio in the forward direction and should comprise a direct gear for use in both passenger vehicles and utility vehicles. In addition, these transmissions should not be characterized by high structural cost and complexity, in particular having a small number of shift elements and avoiding double shifts during sequential shifting processes, so that for shifts in defined gear groups in each case only one shift element is changed.